The present invention relates to systems, and elements, components, and compositions therefor, for monitoring and indicating the elapse of a predetermined integral of ambient conditions, such as time, temperature, humidity, actinic radiation, vaporous atmosphere, and the like, to which such a system has been exposed. Typically, for example in monitoring a thermal ambient, a composition comprising an indicator system is formulated to exhibit a readily discernible property variation, such as a change of color or color density, upon the elapse of a given time-temperature integral, and the system, often in the form of a label, is associated with a product of foodstuff, medicament, or the like the useful shelf life, i.e., the safe or potent utility, of which is known to expire substantially concurrently with the elapse of the given time-temperature integral.
In particular, the present invention relates to improvements in ambient-condition responsive compositions of shelf life systems comprising substituted diacetylenic monomer components which exhibit a distinct color change as a result of and generally concomitant with a solid state polymerization effected by an ambient condition integral; typically, as in the case of a time-temperature indicator (TTI) system, the integral of time and temperature.
Substituted diacetylenic monomers useful in the present invention have been studied and utilized in TTI systems for many years. Such utility of numerous monomers comprising at least two conjugated acetylene groups (—C≡C—C≡C—) and their unique physico-chemical properties, e.g., responsiveness to temperature change by transforming into contrastingly colored solid state polymerization reaction products, have, for instance, been described by Patel et al. (U.S. Pat. No. 3,999,946). The synthesis of these monomers and their implementation in useful TTI and other shelf life indicator compositions are discussed there at length by Patel et al, and continue to be valid in formulating embodiments of the present invention. Likewise, the use of these diacetylenic monomer shelf life system components and improvements thereon, including asymmetric substitutions and complexes, and improved methods of monomer synthesis, have been described at length by Patel (U.S. Pat. No. 4,384,980) and Preziosi et al. (U.S. Pat. No. 4,788,151). Such useful descriptions and examples of diacetylenic monomer components useful in the present invention are incorporated herein by reference.
While the consistent and predictable response of these diacetylenic monomer compositions to thermal stimuli provides a basis for highly functional and reliable TTI system products, a similar contemporary color-generating solid state polymerization response to other ambient actinic stimuli, such as ultraviolet radiation, significantly compromises their utility in such systems. This detraction has been recognized long since even by Patel et al who suggested the use of active ultraviolet light-absorbing compounds, such as benzophenones, benzotriazoles, and the like to mitigate these results. Thus, diacetylenic monomer composition TTI products comprising sheet elements, such as labels or marker tabs, bearing a localized deposit of active monomer indicator composition have had laminated thereto an overlying film comprising a UV-absorbing composition.